Because the point of this is to force friends and adult family members to purchase extra copies of games. Do yall actually think Valve is giving away free game access?
To those who are saying it's not IP locked: people on reddit are all saying that the newer sign-ups are locked but they didn't clear older sharing from early beta.
You need to read The Amazon Anti-Trust Paradox by current FTC head Lina Khan. She argues that the consumer price oriented monopoly definition is old and outdated in the modern setting. Price is not a sufficient proxy for market competitiveness, and in fact, price is often used to kill competitiveness by undercutting new and innovative products.